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Published July 20, 2014 | Submitted + Published
Journal Article Open

Early Excitation of Spin-Orbit Misalignments in Close-in Planetary Systems

Abstract

Continued observational characterization of transiting planets that reside in close proximity to their host stars has shown that a substantial fraction of such objects possess orbits that are inclined with respect to the spin axes of their stars. Mounting evidence for the wide-spread nature of this phenomenon has challenged the conventional notion that large-scale orbital transport occurs during the early epochs of planet formation and is accomplished via planet–disk interactions. However, recent work has shown that the excitation of spin–orbit misalignment between protoplanetary nebulae and their host stars can naturally arise from gravitational perturbations in multi-stellar systems as well as magnetic disk–star coupling. In this work, we examine these processes in tandem. We begin with a thorough exploration of the gravitationally facilitated acquisition of spin–orbit misalignment and analytically show that the entire possible range of misalignments can be trivially reproduced. Moreover, we demonstrate that the observable spin–orbit misalignment only depends on the primordial disk–binary orbit inclination. Subsequently, we augment our treatment by accounting for magnetic torques and show that more exotic dynamical evolution is possible, provided favorable conditions for magnetic tilting. Cumulatively, our results suggest that observed spin–orbit misalignments are fully consistent with disk-driven migration as a dominant mechanism for the origin of close-in planets.

Additional Information

© 2014 The American Astronomical Society. Received 2014 February 8; accepted 2014 June 2; published 2014 July 1. We thank the anonymous referee for a careful review of the paper which led to an enhanced manuscript. During the review of this paper, we have become aware that Lai (2014) arrived at similar results simultaneously and independently. K.B. acknowledges the generous support from the ITC Prize Postdoctoral Fellowship at the Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics. C.S. acknowledges the generous support from the CONOCO Graduate Fellowship in Geology at the California Institute of Technology.

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Published - 0004-637X_790_1_42.pdf

Submitted - 1406.4183v1.pdf

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